1. Field of the Invention
The present invention relates to a stereo image display apparatus and method that allows a user to view stereo images three-dimensionally without using special spectacles such as polarizing spectacles or liquid crystal shutter spectacles, and a storage medium storing a program for implementing the method.
2. Prior Art
Conventional glasses-free type stereo image display apparatuses that do not require the use of special spectacles include 3-D (three-dimensional) displays that use a parallax barrier method and 3-D displays that use a lenticular lens method.
Such 3-D displays use the optical properties of a parallax barrier, lenticular lenses or the like, and are designed such that a left eye image and a right eye image displayed on an image display panel are separated to the left and right respectively, thus allowing a user positioned in a suitable viewing position a certain fixed distance perpendicularly in front of the display to see a 3-D image. If the user views the display from a position away from the suitable viewing position, then the 3-D image will not be seen properly.
The following two methods are known for ensuring that the user is always in a suitable viewing position when viewing the display.
In the first method, movement of the user is detected using sensors, a camera or the like, and the suitable viewing position is shifted in accordance with the viewer's movement. According to this method, the suitable viewing position can be shifted left and right by controlling the parallax barrier or lenticular lenses mechanically or electrically.
However, it is difficult to shift the suitable viewing position forward and backward, and hence the user's movement in the forward/backward direction cannot be followed. Moreover, to realize this method, the mechanism of the apparatus must be made more complex, resulting in increased manufacturing costs.
In the second method, when the user is not in the suitable viewing position, the image displayed is changed in a clearly perceptible way, so that the user realizes that he/she has strayed from the suitable viewing position, and can then move back to the suitable viewing position of his/her own accord. In Japanese Patent No. 2951232, a method is disclosed in which this method is put into practice using a parallax barrier base plate.
However, the above conventional example suffers from the following problems. The method disclosed in Japanese Patent No. 2951232 is intimately linked to the design of the parallax barrier type 3-D display, and hence it is unclear whether the method can also be applied to other types of 3-D display. Moreover, the method must be fixedly incorporated into the 3-D display, thus lowering the degree of design freedom. Furthermore, even if the viewer does not wish to verify the suitable viewing position, this function cannot be “switched off”.